by Tamara Scully
Zoonotic diseases are those which can pass from animals to humans. According to the Centers for Disease Control (CDC), 75% of emerging diseases that threaten human health originate in animals. What common diseases can farm livestock carry that might cause concern to farm families, farm workers and visitors?
Many pathogens can be transmitted via manure. Contact with livestock themselves, their bedding or tools and equipment can spread disease-causing organisms. Some pathogens can be found in soil or water sources. Some of these same livestock diseases can also be transmitted through undercooked meat, resulting in food poisoning. Other diseases can be airborne and inhaled. Still others are transmitted through saliva or other bodily fluids.
Many of these pathogens will cause illness in some livestock, but even healthy livestock with no signs of infection can harbor pathogens that can cause human illness. In other instances, the animals may not show signs of illness yet be able to transmit pathogens.
Here are some common pathogens livestock can transmit to humans:
- Salmonella spp. are often implicated in food poisoning, where handling or eating undercooked poultry or meat results in transmission of the pathogen to humans, causing illness with abdominal cramps, diarrhea and fever. But salmonella can also be transmitted through contact with infected animals or their environment, or equipment or tools used in animal areas. Livestock don’t always show symptoms when they are carriers of salmonella. Pigs can suffer from septicemia caused by salmonella. Some animals do have diarrhea due to the bacteria. Cows, small ruminants and horses can all become infected with various strains of salmonella.
- E. coli is often associated with eating undercooked meat, primarily beef. Deadly pathogenic forms of the bacteria, such as E. coli O157:H7, which produces shiga toxins, have caused lethal food poisoning outbreaks. Livestock can carry various strains of E. coli without illness. Other strains of E. coli will cause animal symptoms, particularly diarrhea.
- Anthrax spores can live in the environment for years. Anthrax can infect livestock and cause death when the animals ingest spores found in soil, water or plants. Spores can then contaminate meat from the animals, causing human illness. The disease can also be spread via contact with sick animals or infected carcasses. Humans can directly contract anthrax from the environment via open wounds, inhalation or ingestion. Vaccinations for livestock are recommended in areas where the pathogen is common.
- Campylobacter spreads similarly to salmonella and causes diarrheal illness in humans. Animals can harbor the bacteria without symptoms, or have diarrhea.
- Brucella bacteria can cause reproductive problems, including abortions or weak offspring, in livestock (although not all infected livestock show symptoms). Human infection is typically via consumption of raw dairy products, or direct contact of the pathogen through animal contact, or infected animal secretions or tissue.
- Leptispira spp. is passed in the urine of infected animals and can live in soil and water for long periods of time. Infected bedding or infected fetal tissue can also be sources of infection. A wide range of livestock can become infected, and may or may not show signs of illness, which can include kidney and liver failure, abortion and fever. Skin wounds or abrasions can allow the disease to spread on contact, or it can spread via ingestion of contaminated soil or water. In humans, it can cause serious kidney or liver failure or meningitis.
- Listeria monocytogenes is primarily transmitted to humans through contaminated meat, soft cheeses, raw milk or certain produce items such as melons. It is not directly transmittable from livestock. Goat, sheep and cattle are primary carriers, and the bacteria can be found in spoiled feed, in soil and in manure. Livestock may be uncoordinated, with paralyzed facial muscles, depression and twisted necks. Abortion and stillbirths can occur.
- Coxiella burnetii causes Q fever in livestock, which typically causes few animal symptoms. It can cause reproductive issues in small ruminants and cattle. Humans acquire the infection via by breathing in dust that has been contaminated with livestock bodily fluids. Raw dairy products are also modes of transmission. In humans, Q fever can become a chronic condition including fever, chills, chest pain, nausea and diarrhea.
- Rabies is fatal for animals and humans and is transmitted via contact with saliva or through animal bites and scratches. Vaccinating cattle, horses and sheep is highly recommended, as animals can spread the virus prior to symptom development.
- Vesticular stomatitis causes blisters to form in mucous membranes, hooves and teats. It is a painful disease. An initial symptom is excessive salivation. It can cause weight loss, dehydration and lameness. Cattle, horses and swine are primarily affected. Biting insects are believed to be a primary mode of transmission, although the disease is also spread via saliva or fluid from ruptured sores from infected animals. In humans, symptoms common to flu-type illnesses occur. Quarantine of infected animals is needed to stop the spread of the disease. Insect control measures and the use of PPE when working with infected animals is required.
- Pseudocowpox causes sores and scabs on cow udders. Direct contact with these sores can transfer the disease, with resulting sores on arms and hands, in humans.
- Ringworm is passed through direct contact with infected animals. It causes circular lesions on the skin. It often occurs in crowded housing conditions, and spores can remain dormant for years in the environment. Cattle, sheep and horses are often affected, and humans can also be affected. Itchy, crusted scabs form on the skin, and nails and hair can be affected.
- Cryptosporidium lives in the gut of infected livestock and is spread via manure. Water sources can become contaminated and spread the disease. Young calves are commonly infected and may or may not have diarrhea. Gastrointestinal symptoms in humans can occur.
Prevention of Zoonotic Transmission
Frequent hand washing and limiting hand-to-face contact can help lower the risk of transmission of many zoonotic diseases. No food, drink, smoking or use of cosmetic items should be permitted in animal barns or areas. Cell phones, pens and other handheld devices should be regularly disinfected if used in animal areas.
Wearing gloves and goggles, donning protective clothing including coveralls or boots, and laundering these at the farm when possible can help decrease the transmission risk of common farm animal pathogens. When handling sick animals, attending births or working with animals with diarrhea, extra precautions should be taken to prevent exposure to bodily fluids and tissues likely to carry infections. Keeping the animal environment clean and free of manure and urine and regular disinfection of tools, equipment and surfaces will reduce the risk of spread to humans.
Respiratory protection may be appropriate when cleaning stalls or during other activities where dust is likely to form, or in confined or crowded housing areas. Diarrhea in livestock should always be considered a sign of a transmittable zoonotic illness.
Work with your vet to appropriately vaccinate livestock, treat for pathogens common to your region and determine which symptoms warrant closer inspection. Worker training on transmittable diseases and proper safety precautions to prevent disease spread should be conducted routinely, including immediately for all new hires.